Introduction to Three Methods for Measuring the Quality of Photodiodes

Distinguish between positive and negative poles
According to the pin arrangement of the photodiode, one foot near the key or colored dot is the positive pole (i.e. P pole), and the other foot is the negative pole (i.e. N pole). For rectangular pipes, marked corners are often made to indicate the direction of the light receiving surface. In general, the long pin is the positive pole.
If the marking of the pipe is blurred, a multimeter can be used for testing and discrimination. Place the multimeter in the Rxlk position, cover the transparent window of the photodiode with a black piece of paper, and connect the red and black probes of the multimeter to either pin of the tube. If the multimeter pointer deviates significantly to the right (10-20k Ω), the pin connected to the black probe will be the positive terminal. If the multimeter pointer does not move during measurement, the pin connected to the black probe is negative.

Quality inspection
The core of a photodiode is mainly made of silicon material. There are three methods to measure the quality of photodiodes.
(1) Resistance measurement method. Using a multimeter with Rx100 or Rxlk settings, just like measuring a regular diode, the forward resistance should be around 10k Ω. When there is no light exposure (you can hold the diode casing by hand), the reverse resistance should be ∞, and then let the photodiode see light. The stronger the light, the smaller the reverse resistance should be. When the light is particularly strong, the reverse resistance can be reduced to below 1k Ω. This kind of pipe is good. If both the forward and reverse resistances are zero or zero, it indicates that the tube is faulty.
(2) Voltage measurement method. Connect the multimeter (pointer type) to the gear below 2.5V DC. The red probe is connected to the positive terminal of the photodiode, and the black probe is connected to the negative terminal. Under sunlight or incandescent light, the voltage is directly proportional to the intensity of the light, generally reaching 0.20-0 45V.
(3) Current measurement method. Set the pointer multimeter to the DC 50uA or 500uA range, with the red probe connected to the positive terminal of the photodiode and the black probe connected to the negative terminal. Under sunlight or incandescent light, the short-circuit current can increase from a few microamperes to several hundred microamperes.